根据短文理解，从A、B、C、D四个选项中选择最佳答案填空。

    After their 15-year-old pet dog died, Rain and his wife, Ann, looked for months to find the right new pet. "I love dogs." said Rain, a worker at a health club in New York. "I can't 1 not having one.

    "Finally, the couple found a lovely young 2 and decided to 3 him home. They named him Little Sheep. Little Sheep quickly made himself at home, sleeping on his new 4 bed at night.

    With heart disease for 25 years, Rain 5 look his medicine four times a day and always had no problems. 6 on March 17, he took the wrong amount(数量) of medicine before he went to sleep. When he got out of bed to 7 the bathroom at night, suddenly, he felt his heart beating fast and later fell to the floor heavily.

    "Little Sheep was usually very 8 and well-behaved," said Ann. "But when my husband hit the floor, the dog gave a loud cry like a wild animal. I was woken but didn't know what was happening. Then l saw my husband 9 on tile bathroom floor. I ran for the 10 and called a hospital at once. "Rain spent several hours in the hospital. By 6:30 a. m., he had been 11 enough to go home. "It surprises me that Little Sheep has such great 12," said his thankful owner. "He's becoming a calm little gentleman. We can walk him on our street, unleashed(未拴住的), without any problem. He's got a lot of 13 now, and everyone wants to 14 him kindly. "

    "We feel the name Little Sheep is not good enough," said Rain. "So now we call him Big Hero, more 15 for an animal of his ability. "